All-solid-state battery and method for manufacturing the same

Abstract

To provide an all-solid-state battery capable of improving the simultaneous sintering property of a solid electrolyte layer and internal electrodes while ensuring an appropriate firing temperature range, and manufacturing method thereof.SOLUTION: An all-solid-state battery 100a includes: a solid electrolyte layer 30 containing oxide-based solid electrolyte as the main component that is represented by the composition formula of Li1+x+2y+aAyM*xM**2-x-yP3O12+c; where, A is a divalent metal element, M* is a trivalent metal element, M** is a tetravalent transition metal, and which has a NASICON type crystal structure that satisfies 0<a<1.4; a first internal electrode 10 containing electrode active material, placed on the first main surface of the solid electrolyte layer; and a second internal electrode 20 placed on the second main surface of the solid electrolyte layer, which contains electrode active material.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an all-solid-state battery and a method for manufacturing the same. [Background technology]

[0002] Lithium-ion secondary batteries are used in a variety of fields, including consumer electronics, industrial machinery, and automobiles. However, lithium-ion secondary batteries containing electrolytes pose risks such as electrolyte leakage, smoke emission, and fire. Therefore, there is a strong focus on developing all-solid-state lithium-ion secondary batteries, particularly those employing oxide-based solid electrolytes that are stable in the atmosphere. For example, all-solid-state batteries using solid electrolytes containing a NASICON-type crystal structure have been disclosed (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2018-73554 [Patent Document 2] Japanese Patent Publication No. 2016-1598 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Oxide-based solid electrolytes containing a NASICON-type crystal structure are formed, for example, by a sintering process in order to obtain desired properties. Further, since co-firing with an internal electrode is required, if there is a deviation in the sintering behavior between members, cracks and delamination are likely to occur. Also, due to the interdiffusion reaction during co-firing, segregation of some substances and unevenness in density occur between the solid electrolyte layer and the internal electrode, and it is more likely to occur significantly as the firing temperature increases. For example, if an electrode active material having an olivine-type crystal structure and elements contained in the electrode active material diffuse or segregate into the solid electrolyte layer, there is a concern that that portion may malfunction and become a cause of a leakage path. Furthermore, the generation of sparse portions due to a deviation in sinterability or reaction between members also inhibits the formation of an ion conduction path at that location and an electron conduction path in the internal electrode, which may lead to deterioration of characteristics and reliability. For the above reasons, it is desirable in design to match the sinterability in the lowest temperature range possible. On the other hand, if an attempt is made to match the sinterability, there is a risk that the appropriate firing temperature range will become narrow.

[0005] An object of the present invention is to provide an all-solid-state battery and a method for manufacturing the same that can improve the co-sinterability of a solid electrolyte layer and an internal electrode while ensuring an appropriate firing temperature range.

Means for Solving the Problems

[0006] The all-solid-state battery according to the present invention has a composition formula of Li 1+x+2y+a A y M´ x M´´ 2-x-y P3O 12+c represented by, where "A" is a divalent metal element, "M'" is a trivalent metal element, "M"" is a tetravalent transition metal, and an oxide-based solid electrolyte having a NASICON-type crystal structure satisfying 0 < a < 1.4 as a main component, a first internal electrode provided on a first main surface of the solid electrolyte layer and containing an electrode active material, and a second internal electrode provided on a second main surface of the solid electrolyte layer and containing an electrode active material.

[0007] In the composition formula of the all-solid-state battery, "x" may be 0 or more and 0.7 or less.

[0008] In the composition formula of the all-solid-state battery, "y" may be 0 or more and 0.3 or less.

[0009] In the composition formula of the all-solid-state battery, "A" may contain at least any one of Ni, Mg, Ca, and Ba.

[0010] In the composition formula of the all-solid-state battery, "M'" may contain at least any one of Al, Y, Ga, and La.

[0011] In the composition formula of the all-solid-state battery, "M''" may contain at least any one of Ge and Zr.

[0012] The method for manufacturing an all-solid-state battery according to the present invention has a composition formula of Li 1+x+2y+a A y M' x M'' 2-x-y P3O 12+c represented by, where "A" is a divalent metal element, "M'" is a trivalent metal element, "M''" is a tetravalent transition metal, and a green sheet containing a powder of an oxide-based solid electrolyte having a NASICON-type crystal structure satisfying 0 < a < 1.4, a paste coating for a first electrode layer formed on the first main surface of the green sheet and containing an electrode active material, and a paste coating for a second electrode layer formed on the second main surface of the green sheet and containing an electrode active material, and a step of preparing a laminate having the laminate, and a step of firing the laminate. [[ID=3A]]

Advantages of the Invention

[0013] According to the present invention, it is possible to provide an all-solid-state battery and a method for manufacturing the same that can improve the co-sinterability of the solid electrolyte layer and the internal electrode while ensuring an appropriate firing temperature range.

Brief Description of the Drawings

[0014] [Figure 1] This is a schematic cross-sectional view showing the basic structure of an all-solid-state battery. [Figure 2] This is a schematic cross-sectional view of a stacked all-solid-state battery. [Figure 3] This is another example of a stacked solid-state battery. [Figure 4] This diagram illustrates a flow chart of the manufacturing process for all-solid-state batteries. [Figure 5] (a) and (b) are diagrams illustrating the lamination process. [Modes for carrying out the invention]

[0015] The embodiments will be described below with reference to the drawings.

[0016] (Embodiment) Figure 1 is a schematic cross-sectional view showing the basic structure of an all-solid-state battery 100. As illustrated in Figure 1, the all-solid-state battery 100 has a structure in which a solid electrolyte layer 30 is sandwiched between a first internal electrode 10 and a second internal electrode 20. The first internal electrode 10 is formed on the first main surface of the solid electrolyte layer 30. The second internal electrode 20 is formed on the second main surface of the solid electrolyte layer 30.

[0017] When the all-solid-state battery 100 is used as a secondary battery, one of the first internal electrode 10 and the second internal electrode 20 is used as the positive electrode and the other as the negative electrode. In this embodiment, as an example, the first internal electrode 10 is used as the positive electrode and the second internal electrode 20 is used as the negative electrode.

[0018] The solid electrolyte layer 30 has a NASICON-type crystal structure and is mainly composed of an oxide-based solid electrolyte having ionic conductivity. The solid electrolyte of the solid electrolyte layer 30 is, for example, an oxide-based solid electrolyte having lithium ion conductivity. This solid electrolyte is, for example, a phosphate-based solid electrolyte. A phosphate-based solid electrolyte having a NASICON-type crystal structure has the properties of high conductivity and stability in the atmosphere. The phosphate-based solid electrolyte is, for example, a lithium-containing phosphate. This phosphate is not particularly limited, but examples include a composite lithium phosphate salt with Ti (e.g., LiTi2(PO4)3). Alternatively, Ti can be partially or completely substituted with a tetravalent transition metal such as Ge, Sn, Hf, or Zr. Furthermore, to increase the Li content, it may be partially substituted with a trivalent transition metal such as Al, Ga, In, Y, or La. More specifically, for example, Li 1+x Al x Ge 2-x (PO4)3 and Li 1+x Al x Zr 2-x (PO4)3, Li 1+x Al x Ti 2-x Examples include (PO4)3. For example, a Li-Al-Ge-PO4 system material is preferred in which the same transition metal as the transition metal contained in the olivine-type crystal structure phosphate contained in the first internal electrode 10 and the second internal electrode 20 is pre-added. For example, if the first internal electrode 10 and the second internal electrode 20 contain a phosphate containing Co and Li, it is preferable that the solid electrolyte layer 30 contains a Li-Al-Ge-PO4 system material with Co pre-added. In this case, the effect of suppressing the elution of the transition metal contained in the electrode active material into the electrolyte can be obtained. If the first internal electrode 10 and the second internal electrode 20 contain a phosphate containing a transition element other than Co and Li, it is preferable that the solid electrolyte layer 30 contains a Li-Al-Ge-PO4 system material with the transition metal pre-added.

[0019] The first internal electrode 10, used as the positive electrode, contains a material having an olivine-type crystal structure as the electrode active material. It is preferable that the second internal electrode 20 also contains the same electrode active material. Examples of such electrode active materials include phosphates containing a transition metal and lithium. The olivine-type crystal structure is found in natural olivine and can be identified by X-ray diffraction.

[0020] Typical examples of electrode active materials with an olivine-type crystal structure include LiCoPO4 containing Co. Phosphates in which the transition metal Co is replaced in this chemical formula can also be used. Here, the ratio of Li and PO4 may vary depending on the valency. It is preferable to use Co, Mn, Fe, Ni, etc. as the transition metal.

[0021] Electrode active materials having an olivine-type crystal structure act as positive electrode active materials in the first internal electrode 10, which acts as the positive electrode. For example, if the electrode active material having an olivine-type crystal structure is contained only in the first internal electrode 10, then this electrode active material acts as the positive electrode active material. When the electrode active material having an olivine-type crystal structure is also contained in the second internal electrode 20, which acts as the negative electrode, although the mechanism of action is not fully understood, it is presumed that this is based on the formation of a partial solid solution state with the negative electrode active material, resulting in an increase in discharge capacity and an increase in the operating potential associated with discharge.

[0022] When both the first internal electrode 10 and the second internal electrode 20 contain electrode active materials having an olivine-type crystal structure, each electrode active material preferably contains a transition metal that may be the same or different from each other. "May be the same or different from each other" means that the electrode active materials contained in the first internal electrode 10 and the second internal electrode 20 may contain the same type of transition metal, or they may contain different types of transition metals. The first internal electrode 10 and the second internal electrode 20 may contain only one type of transition metal, or they may contain two or more types of transition metals. Preferably, the first internal electrode 10 and the second internal electrode 20 contain the same type of transition metal. More preferably, the electrode active materials contained in both electrodes have the same chemical composition. The inclusion of the same type of transition metal or the same composition of electrode active materials in the first internal electrode 10 and the second internal electrode 20 increases the similarity of the compositions of both internal electrode layers, which has the effect of allowing the all-solid-state battery 100 to withstand actual use without malfunction, depending on the application, even if the terminals are connected in reverse polarity.

[0023] The second internal electrode 20 contains a negative electrode active material. By containing the negative electrode active material in only one electrode, it becomes clear that the electrode in question acts as the negative electrode and the other electrode acts as the positive electrode. Alternatively, both electrodes may contain a known substance as the negative electrode active material. Regarding the negative electrode active material of the electrodes, prior art in secondary batteries can be appropriately referenced, and examples include compounds such as titanium oxide, lithium titanium composite oxide, lithium titanium composite phosphate, carbon, and lithium vanadium phosphate.

[0024] In the fabrication of the first internal electrode 10 and the second internal electrode 20, in addition to these electrode active materials, an ionic conductive solid electrolyte and a conductive material (conductive additive) are added. For these components, an internal electrode paste can be obtained by uniformly dispersing a binder and a plasticizer in water or an organic solvent. The conductive additive may include carbon materials. The conductive additive may also include metals. Examples of metals used as conductive additives include Pd, Ni, Cu, Fe, and alloys containing these. The solid electrolyte contained in the first internal electrode 10 and the second internal electrode 20 can be, for example, the same as the main component solid electrolyte of the solid electrolyte layer 30.

[0025] Figure 2 is a schematic cross-sectional view of a stacked all-solid-state battery 100a, in which multiple battery units are stacked. The all-solid-state battery 100a comprises a stacked chip 60 having a substantially rectangular parallelepiped shape. In the stacked chip 60, a first external electrode 40a and a second external electrode 40b are provided so as to be in contact with two side surfaces, which are two of the four surfaces other than the top and bottom surfaces at the stacking direction ends. These two side surfaces may be adjacent to each other or may be two opposing sides. In this embodiment, the first external electrode 40a and the second external electrode 40b are provided so as to be in contact with two opposing side surfaces (hereinafter referred to as two end surfaces).

[0026] In the following description, components having the same composition range, thickness range, and particle size distribution range as the all-solid-state battery 100 will be given the same reference numerals, and detailed explanations will be omitted.

[0027] In the all-solid-state battery 100a, multiple first internal electrodes 10 and multiple second internal electrodes 20 are alternately stacked via a solid electrolyte layer 30. The edges of the multiple first internal electrodes 10 are exposed on the first end face of the stacked chip 60, but not on the second end face. The edges of the multiple second internal electrodes 20 are exposed on the second end face of the stacked chip 60, but not on the first end face. As a result, the first internal electrodes 10 and the second internal electrodes 20 are alternately conductive to the first external electrode 40a and the second external electrode 40b. The solid electrolyte layer 30 extends from the first external electrode 40a to the second external electrode 40b. Thus, the all-solid-state battery 100a has a structure in which multiple battery units are stacked.

[0028] A cover layer 50 is laminated on the upper surface of the laminated structure of the first internal electrode 10, the solid electrolyte layer 30, and the second internal electrode 20 (in the example in Figure 2, the upper surface of the first internal electrode 10, which is the uppermost layer). A cover layer 50 is also laminated on the lower surface of the laminated structure (in the example in Figure 2, the lower surface of the first internal electrode 10, which is the lowest layer). The cover layer 50 is mainly composed of an inorganic material containing, for example, Al, Zr, or Ti (e.g., Al2O3, ZrO2, TiO2, etc.). The cover layer 50 may also mainly contain the main components of the solid electrolyte layer 30.

[0029] The first internal electrode 10 and the second internal electrode 20 may be provided with a current collector layer. For example, as illustrated in Figure 3, a first current collector layer 11 may be provided within the first internal electrode 10. Also, a second current collector layer 21 may be provided within the second internal electrode 20. The first current collector layer 11 and the second current collector layer 21 are mainly composed of a conductive material. For example, metal, carbon, etc. can be used as the conductive material for the first current collector layer 11 and the second current collector layer 21. By connecting the first current collector layer 11 to the first external electrode 40a and the second current collector layer 21 to the second external electrode 40b, the current collection efficiency is improved.

[0030] The solid electrolyte layer 30, mainly composed of an oxide-based solid electrolyte having a NASICON-type crystal structure, is formed, for example, by a sintering process to obtain desired properties. Since co-firing of the solid electrolyte layer 30 with the first internal electrode 10 and the second internal electrode 20 is necessary, discrepancies in sintering behavior between the components can easily lead to cracks and delamination. Furthermore, due to interdiffusion reactions during co-firing, segregation of some substance and uneven density occur between the solid electrolyte layer 30 and the first internal electrode 10 and the second internal electrode 20, and these tend to become more pronounced with higher firing temperatures. For example, if an electrode active material having an olivine-type crystal structure, or elements contained in the electrode active material, diffuses or segregates within the solid electrolyte layer 30, there is a concern that the segregated portion will operate and become a cause of leak paths. In addition, the occurrence of sparse areas due to discrepancies in sinterability or reactions between components is also a concern, as it hinders the formation of ion conduction paths and electron conduction paths within the internal electrodes in those areas, leading to a deterioration of properties and reliability. Therefore, it is desirable to match the sinterability between the solid electrolyte layer 30 and the first internal electrode 10 and the second internal electrode 20 in the low-temperature range. On the other hand, attempting to match the sinterability may narrow the appropriate firing temperature range.

[0031] Therefore, in this embodiment, the oxide-based solid electrolyte having a NASICON-type crystal structure, which is the main component of the solid electrolyte layer 30, contains an excess of Li relative to its stoichiometric composition. Since Li has the effect of lowering the sintering start temperature, Compared to the case where an oxide-based solid electrolyte with a stoichiometric composition is used, the sintering start temperature of the solid electrolyte layer 30 can be lowered. This improves the simultaneous sintering between the solid electrolyte layer 30 and the first internal electrode 10 and the second internal electrode 20. In this embodiment, "improved simultaneous sintering" is defined as "when the solid electrolyte layer 30 and the first internal electrode 10 and the second internal electrode are co-fired, the porosity of both can be reduced."

[0032] On the other hand, if the addition amount of Li becomes excessive, in terms of material design, the sintering temperature of the solid electrolyte layer 30 drops too much downward, and due to the difference in shrinkage, defects such as cracks and interlayer delamination are likely to occur. In addition, the co-sintering temperature range in which the co-sintering property between the solid electrolyte layer 30, the first internal electrode 10, and the second internal electrode becomes good becomes very narrow, making it difficult to apply from the perspective of productivity in the firing process. The co-sintering temperature range refers to the width of the highest temperature maintained in the firing process.

[0033] As a result of the intensive research by the present inventors, when an oxide-based solid electrolyte having a NASICON-type crystal structure is expressed as in the following formula (1), when 0 < a < 1.4, without narrowing the appropriate firing temperature range of the solid electrolyte layer 30, it has been found that the co-sintering property between the solid electrolyte layer 30, the first internal electrode 10, and the second internal electrode 20 is improved. In the following formula (1), "A" is a divalent metal element. "M'" is a trivalent metal element. "M''" is a tetravalent transition metal. Li 1+x+2y+a A y M´ x M´´ 2-x-y P3O 12+c (1)

[0034] From the perspective of sufficiently reducing the sintering start temperature of the oxide-based solid electrolyte having a NASICON-type crystal structure, "a" in the above formula (1) is preferably 0.1 or more, and more preferably 0.3 or more. From the perspective of sufficiently widening the firing temperature range suitable for densification of the solid electrolyte layer 30, "a" in the above formula (1) is preferably 1.3 or less, and more preferably 1.0 or less.

[0035] In the above formula (1), if "x" is large, the element M'' that contributes to the formation of the basic framework of the NASICON crystal structure decreases, which may lead to a decrease in battery performance due to the generation of unexpected by-products that obstruct the conduction path of Li ions. Therefore, it is preferable to set an upper limit on "x". In this embodiment, for example, "x" is preferably 0.7 or less, more preferably 0.6 or less, and even more preferably 0.5 or less.

[0036] In the above formula (1), if "x" is small, the number of Li ions contributing as carriers in the solid electrolyte decreases, which may lead to a decrease in ionic conductivity and a deterioration in battery performance. Therefore, it is preferable to set a lower limit for "x". In this embodiment, for example, "x" is preferably 0 or greater, more preferably 0.1 or greater, and even more preferably 0.2 or greater.

[0037] In the above formula (1), if "y" is large, the element M'' that contributes to the formation of the basic framework of the NASICON crystal structure decreases, which may lead to a decrease in battery performance due to the generation of unexpected by-products that obstruct the conduction path of Li ions. Therefore, it is preferable to set an upper limit on "y". In this embodiment, for example, "y" is preferably 0.3 or less, more preferably 0.25 or less, and even more preferably 0.2 or less.

[0038] In the above formula (1), if "y" is small, the number of Li ions contributing as carriers in the solid electrolyte decreases, which may lead to a decrease in ionic conductivity and a deterioration in battery performance. Therefore, it is preferable to set a lower limit for "y". In this embodiment, for example, "y" is preferably 0 or greater, more preferably 0.05 or greater, and even more preferably 0.1 or greater.

[0039] In the above formula (1), "A" is a divalent element that can be partially substituted at the tetravalent site of M''. Therefore, Ni, Mg, Ca, Ba, etc. are preferable. By substituting elements with different valences, the content of Li ions in the solid electrolyte can be increased. Similarly, since "M'" is a trivalent element that can be partially substituted at the site of M'', Al, Y, Ga, La, etc. are preferable. "M''" is preferably Ge, Zr, etc., which are known elements capable of forming a stable phosphate-based NASICON framework.

[0040] Incidentally, the thicknesses of the first internal electrode 10 and the second internal electrode 20 are 0.1 μm or more and 500 μm or less, 0.5 μm or more and 300 μm or less, and 1 μm or more and 300 μm or less. The thickness of the solid electrolyte layer 30 in the region sandwiched by the first internal electrode 10 and the second internal electrode 20 is 0.1 μm or more and 100 μm or less, 0.5 μm or more and 50 μm or less, and 1 μm or more and 20 μm or less.

[0041] Subsequently, the manufacturing method of the all-solid-state battery 100a illustrated in FIG. 2 will be described. FIG. 4 is a diagram illustrating the flow of the manufacturing method of the all-solid-state battery 100a.

[0042] (Process for producing raw material powder for solid electrolyte layer) First, the raw material powder for the solid electrolyte layer constituting the above-mentioned solid electrolyte layer 30 is produced. For example, by mixing raw materials, additives, etc. and using a solid-phase synthesis method or the like, a raw material powder of an oxide-based solid electrolyte having a crystal structure satisfying 0 < a < 1.4 in the above formula (1) can be produced. The obtained raw material powder can be adjusted to a desired average particle size by dry pulverization. For example, it is adjusted to a desired average particle size using a planetary ball mill with 5 mmφ ZrO2 balls.

[0043] (Process for producing raw material powder for cover layer) First, the raw material powder for the ceramics constituting the cover layer 50 is prepared. For example, raw materials and additives can be mixed and a solid-phase synthesis method can be used to produce the raw material powder for the cover layer. The obtained raw material powder can be adjusted to the desired average particle size by dry grinding. For example, the desired average particle size can be adjusted using a planetary ball mill with 5 mmφ ZrO2 balls. If the solid electrolyte layer 30 and the cover layer 50 have the same composition, the raw material powder for the solid electrolyte layer can be used as a substitute.

[0044] (Process for preparing paste for internal electrodes) Next, an internal electrode paste is prepared for the fabrication of the first internal electrode 10 and the second internal electrode 20 described above. For example, an internal electrode paste can be obtained by uniformly dispersing a conductive additive, electrode active material, solid electrolyte material, sintering aid, binder, plasticizer, etc., in water or an organic solvent. The solid electrolyte paste described above may be used as the solid electrolyte material. Carbon materials may be used as the conductive additive. Metals may also be used as the conductive additive. Examples of metals used as conductive additives include Pd, Ni, Cu, Fe, and alloys containing these. Pd, Ni, Cu, Fe, alloys containing these, and various carbon materials may be used further. If the composition of the first internal electrode 10 and the second internal electrode 20 is different, each internal electrode paste may be prepared individually.

[0045] The paste for internal electrodes contains, for example, one or more glass components such as Li-BO compounds, Li-Si-O compounds, Li-CO compounds, Li-SO compounds, and Li-PO compounds as sintering aids.

[0046] (Process for preparing paste for external electrodes) Next, an external electrode paste is prepared for the fabrication of the first external electrode 40a and the second external electrode 40b described above. For example, an external electrode paste can be obtained by uniformly dispersing a conductive material, glass frit, binder, plasticizer, etc., in water or an organic solvent.

[0047] (Solid electrolyte green sheet manufacturing process) A solid electrolyte slurry having a desired average particle size is obtained by uniformly dispersing raw material powder for the solid electrolyte layer in an aqueous solvent or organic solvent together with a binder, dispersant, plasticizer, etc., and then performing wet grinding. At this time, a bead mill, wet jet mill, various kneaders, high-pressure homogenizer, etc. can be used, and it is preferable to use a bead mill from the viewpoint that particle size distribution adjustment and dispersion can be performed simultaneously. A binder is added to the obtained solid electrolyte slurry to obtain a solid electrolyte paste. A solid electrolyte green sheet 51 can be produced by coating with the obtained solid electrolyte paste. The coating method is not particularly limited, and a slot die method, reverse coating method, gravure coating method, bar coating method, doctor blade method, etc. can be used. The particle size distribution after wet grinding can be measured, for example, using a laser diffraction measuring device using the laser diffraction scattering method.

[0048] (Lamination process) As illustrated in Figure 5(a), an internal electrode paste 52 is printed on one surface of the solid electrolyte green sheet 51. The thickness of the internal electrode paste 52 is equal to or greater than the thickness of the solid electrolyte green sheet 51. A reverse pattern 53 is printed on the areas of the solid electrolyte green sheet 51 where the internal electrode paste 52 is not printed. The same reverse pattern 53 as that of the solid electrolyte green sheet 51 can be used. Multiple printed solid electrolyte green sheets 51 are stacked alternately with a slight offset. As illustrated in Figure 5(b), a laminate is obtained by pressing a cover sheet 54 onto the top and bottom of the stacking direction. In this case, a laminate with a roughly rectangular parallelepiped shape is obtained such that the internal electrode paste 52 is alternately exposed on two end faces of the laminate. The cover sheet 54 can be formed by coating it with raw material powder for the cover layer using the same method as in the solid electrolyte green sheet manufacturing process. The cover sheet 54 is formed to be thicker than the solid electrolyte green sheet 51. It may be made thicker during coating, or by stacking multiple coated sheets.

[0049] Next, the external electrode paste 55 is applied to each of the two end faces using a dipping method or the like, and then dried. This yields a molded body for forming the all-solid-state battery 100a.

[0050] (Firing process) Next, the resulting laminate is fired. The firing conditions are under an oxidizing or non-oxidizing atmosphere, and the maximum temperature is preferably 400°C to 1000°C, more preferably 500°C to 900°C, but there are no particular limitations. To sufficiently remove the binder before reaching the maximum temperature, a step may be included in which the laminate is held at a temperature lower than the maximum temperature in an oxidizing atmosphere. To reduce process costs, it is desirable to fire at the lowest possible temperature. After firing, a re-oxidation treatment may be performed. Through the above steps, an all-solid-state battery 100a is produced.

[0051] Furthermore, by sequentially layering the internal electrode paste, the current collector paste containing a conductive material, and the internal electrode paste, a current collector layer can be formed within the first internal electrode 10 and the second internal electrode 20. [Examples]

[0052] A solid-state battery was fabricated according to the following embodiment, and its characteristics were investigated.

[0053] (Example 1) A sintering aid was added to a phosphate-based solid electrolyte having a predetermined particle size, and the mixture was dispersed in a dispersion medium to prepare a solid electrolyte slurry. A binder was added to the obtained solid electrolyte slurry to prepare a solid electrolyte paste. A green sheet was prepared by coating it with the solid electrolyte paste. Li was used as the phosphate-based solid electrolyte. 1.7 Mg 0.05 Al 0.3 Ge 1.65 P3O 12+c Li was used. 1+x+2y+a A y M' x M'´ 2-x-y P3O 12+c Expressed as follows, "a" is 0.3, "x" is 0.3, and "y" is 0.05.

[0054] The electrode active material and solid electrolyte material were highly dispersed using a wet bead mill or the like to produce a ceramic paste consisting solely of ceramic particles. Next, the ceramic paste and conductive material were thoroughly mixed to produce a paste for the internal electrodes.

[0055] A paste for the internal electrodes was printed onto a solid electrolyte green sheet using a screen with a predetermined pattern. 100 of these printed sheets were stacked, offset from each other so that the electrodes were pulled out from the left and right.

[0056] A sintering aid was added to a phosphate-based solid electrolyte having a predetermined particle size, and the mixture was dispersed in a dispersion medium to prepare a solid electrolyte slurry. A binder was added to the obtained solid electrolyte slurry to prepare a paste for cover sheets. A cover sheet was prepared by coating it with the paste for cover sheets.

[0057] Solid electrolyte green sheets were stacked and attached to the top and bottom as cover layers, then pressed together using a heat-pressure press, and the laminate was cut to a predetermined size using a dicer. This resulted in a laminate with a roughly rectangular parallelepiped shape. On each of the two end faces of the laminate where the internal electrode paste was exposed, the external electrode paste was applied by a dip method or the like and dried. After that, it was degreased by heat treatment at a temperature of 300°C to 500°C, and then sintered by heat treatment in a temperature range of 500°C to 900°C to produce a sintered body.

[0058] (Example 2) As a phosphate-based solid electrolyte, Li 1.7 Mg 0.1 Al 0.3 Ge 1.6 P3O 12+c Except for the use of Li, the conditions were the same as in Example 1. 1+x+2y+a A y M' x M'´ 2-x-y P3O 12+c Expressed as follows, "a" is 0.2, "x" is 0.3, and "y" is 0.1.

[0059] (Example 3) As a phosphate-based solid electrolyte, Li 1.44 Mg 0.02 Al 0.3 Ge 1.68 P3O 12+c Except for the use of Li, the conditions were the same as in Example 1. 1+x+2y+a A y M' x M'´ 2-x-y P3O 12+c Expressed as follows, "a" is 0.1, "x" is 0.3, and "y" is 0.02.

[0060] (Example 4) As a phosphate-based solid electrolyte, Li 1.7 Ba 0.05 Al 0.3 Ge 1.65 P3O 12+c Except for the use of Li, the conditions were the same as in Example 1. 1+x+2y+a A y M' x M'´ 2-x-y P3O 12+c Expressed as follows, "a" is 0.3, "x" is 0.3, and "y" is 0.05.

[0061] (Example 5) As a phosphate-based solid electrolyte, Li 1.8 Mg 0.05 Al 0.5 Ge 1.45 P3O 12+c Except for the use of Li, the conditions were the same as in Example 1. 1+x+2y+a A y M' x M'´ 2-x-y P3O 12+c Expressed as follows, "a" is 0.2, "x" is 0.5, and "y" is 0.05.

[0062] (Example 6) As a phosphate-based solid electrolyte, Li 1.7 Mg 0.05 Al 0.5 Ge 1.45 P3O 12+c Except for the use of Li, the conditions were the same as in Example 1.1+x+2y+a A y M´ x M´´ 2-x-y P3O 12+c When expressed as, "a" is 0.1, "x" is 0.5, and "y" is 0.05.

[0063] (Example 7) As the phosphate-based solid electrolyte, Li 2.2 Mg 0.05 Al 0.8 Ge 1.15 P3O 12+c Except for using this, the same conditions as in Example 1 were used. Li 1+x+2y+a A y M´ x M´´ 2-x-y P3O 12+c When expressed as, "a" is 0.3, "x" is 0.8, and "y" is 0.05.

[0064] (Example 8) As the phosphate-based solid electrolyte, Li 2.2 Mg 0.4 Al 0.3 Ge 1.3 P3O 12+c Except for using this, the same conditions as in Example 1 were used. Li 1+x+2y+a A y M´ x M´´ 2-x-y P3O 12+c When expressed as, "a" is 0.1, "x" is 0.3, and "y" is 0.4.

[0065] (Comparative Example 1) As the phosphate-based solid electrolyte, Li 1.3 Al 0.3 Ge 1.7 P3O 12+c Except for using this, the same conditions as in Example 1 were used. Li 1+x+2y+a A y M´ x M´´ 2-x-y P3O 12+c When expressed as, "a" is 0, "x" is 0.3, and "y" is 0.

[0066] (Comparative Example 2) As a phosphate-based solid electrolyte, Li 1.1 Mg 0.05 Al 0.3 Ge 1.65 P3O 12+c Except for the use of Li, the conditions were the same as in Example 1. 1+x+2y+a A y M' x M'´ 2-x-y P3O 12+c Expressed as follows, "a" is -0.3, "x" is 0.3, and "y" is 0.05.

[0067] (Comparative Example 3) As a phosphate-based solid electrolyte, Li 2.8 Mg 0.05 Al 0.3 Ge 1.65 P3O 12+c Except for the use of Li, the conditions were the same as in Example 1. 1+x+2y+a A y M' x M'´ 2-x-y P3O 12+c Expressed as follows, "a" is 1.4, "x" is 0.3, and "y" is 0.05.

[0068] (Comparative Example 4) As a phosphate-based solid electrolyte, Li 1.5 Al 0.5 Ge 1.5 P3O 12+c Except for the use of Li, the conditions were the same as in Example 1. 1+x+2y+a A y M' x M'´ 2-x-y P3O 12+c Expressed as such, "a" is 0, "x" is 0.5, and "y" is 0.

[0069] Table 1 shows the compositions of the phosphate-based solid electrolytes used in Examples 1 to 8 and Comparative Examples 1 to 4. [Table 1]

[0070] (Analysis of simultaneous sintering properties) Simultaneous sinterability was investigated for each of Examples 1 to 8 and Comparative Examples 1 to 4. Specifically, the porosity of the solid electrolyte layer 30 after firing was measured, and the overall porosity was measured and evaluated. For all-solid-state batteries obtained by alternately stacking internal electrodes and solid electrolyte layers, cross-section processing was performed using a cross-section polisher (CP), and secondary electron images were acquired at 10 locations for each of the solid electrolyte layer and internal electrodes using a scanning electron microscope (Hitachi High-Tech Corporation, model: S-4800) at an acceleration voltage of 5kV and the same magnification. The average occupancy rate of the pore area of ​​each layer was measured by image analysis, and the porosity of the solid electrolyte layer and internal electrodes was measured separately. The porosity value obtained by summing the measured values ​​of both layers was defined as the overall porosity and calculated accordingly.

[0071] If the total porosity was less than 5%, the co-sintering properties were judged as good ("○"). If the total porosity was 5% or more but less than 10%, the co-sintering properties were judged as somewhat good ("△"). If the total porosity was 10% or more, the co-sintering properties were judged as poor ("×").

[0072] (Analysis of the appropriate co-firing temperature range) For each of Examples 1 to 8 and Comparative Examples 1 to 4, the appropriate range of co-firing temperatures was investigated. Specifically, laminates obtained after the degreasing process by alternately stacking electrode layers and solid electrolyte layers were prepared, and the firing temperature was varied. The firing temperature at which the best overall porosity was obtained was used as the reference, and the firing temperature range in which the decrease in overall porosity was 5% or less was defined as the appropriate co-firing temperature range and evaluated.

[0073] If the range of simultaneous firing temperatures was ±10°C or more, the simultaneous firing temperature range was judged as good ("○"). If the range of simultaneous firing temperatures was ±5°C or more but less than 10°C, the simultaneous firing temperature range was judged as somewhat good ("△"). If the range of simultaneous firing temperatures was less than ±5°C, the simultaneous firing temperature range was judged as poor ("×").

[0074] (Analysis of battery characteristics) The battery characteristics were investigated for each of Examples 1 to 8 and Comparative Examples 1 to 4. Specifically, the initial Coulomb efficiency was measured, and the capacity retention rate after 100 cycles was measured. The initial Coulomb efficiency was determined by performing a charge-discharge test at room temperature, with a value of 10 μA / cm². 2 The battery was charged to 2.7V at a given current density, then paused for 10 minutes, and discharged to 0V at the same current density. The initial charge and discharge capacities were measured, and the initial Coulomb efficiency was defined and evaluated by dividing the initial discharge capacity by the initial charge capacity. In addition, measurements were taken for 100 cycles under the same charge and discharge conditions, and the capacity retention rate after 100 cycles was defined and evaluated by dividing the discharge capacity after 100 cycles by the initial discharge capacity.

[0075] If the initial Coulomb efficiency was 80% or higher, it was judged as "Excellent" (◎). If the initial Coulomb efficiency was 60% or higher but less than 80%, it was judged as "Good" (〇). If the initial Coulomb efficiency was 30% or higher but less than 60%, it was judged as "Somewhat Good" (△). If the initial Coulomb efficiency was less than 30%, it was judged as "Poor" (×).

[0076] (Overall assessment) If any of the simultaneous sintering properties, simultaneous firing temperature range, and battery characteristics were judged as good ("〇") or very good ("◎"), the overall judgment was judged as good ("〇"). If there were no defects ("×") and one or more slightly good ("△") in simultaneous sintering properties, simultaneous firing temperature range, and battery characteristics, the overall judgment was judged as slightly good ("△"). If there was one or more defects ("×") in simultaneous sintering properties, simultaneous firing temperature range, and battery specificity, the overall judgment was judged as poor ("×"). The results are shown in Table 2. [Table 2]

[0077] In any of Examples 1 to 8, the co-sinterability was determined to be good "〇" or slightly good "△". This is presumably because 0 < a < 1.4 was satisfied in the above formula (1) and Li was excessive with respect to the stoichiometric composition. Next, in any of Examples 1 to 8, the co-firing temperature range was determined to be good "〇" or slightly good "△". This is presumably because 0 < a < 1.4 was satisfied in the above formula (1) and Li did not become excessively large. In any of Examples 1 to 8, the battery characteristics were also determined to be very good "◎", good "〇" or slightly good "△". This is presumably because the co-sinterability was good "〇" or slightly good "△".

[0078] In any of Comparative Examples 1, 2, and 4, the co-sinterability was determined to be poor "×". This is presumably because the relationship of 0 < a < 1.4 was not satisfied in the above formula (1) and the sintering start temperature of the solid electrolyte layer 30 did not decrease. For Comparative Example 3, the co-firing temperature range was determined to be poor "×". This is presumably because 0 < a < 1.4 was not satisfied in the above formula (1) and Li was excessively large.

[0079] Regarding Examples 7 and 8, the battery characteristics of Examples 1 to 6 resulted in good results. This is presumably because in Examples 1 to 6, 0 < a < 1.4 was satisfied in the above formula (1), and 0 ≤ x ≤ 0.7 and 0 ≤ y ≤ 0.3 were satisfied.

[0080] " Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

Explanation of Reference Numerals

[0081] 10 First internal electrode 11 First current collector layer 20 Second internal electrode 21 Second current collector layer 30 Solid electrolyte layer 40a First external electrode 40b 2nd external electrode 50 Cover Layer 51 Solid Electrolyte Green Sheet 52 Paste for internal electrodes 53 Reverse Pattern 54 Cover Sheets 55 Paste for external electrodes 60-layer chip 100,100a all solid state battery

Claims

1. The empirical formula is Li １＋ｘ＋２ｙ＋ａ A ｙ M' ｘ M'´ ２－ｘ－ｙ P ３ O １２＋ｃ A solid electrolyte layer mainly composed of an oxide-based solid electrolyte having a NASICON-type crystal structure satisfying 0.1 ≤ a ≤ 0.3, 0.3 ≤ x ≤ 0.8, and 0.02 ≤ y ≤ 0.4, where "A" is either Mg or Ba, "M'" is Al, and "M''" is Ge, A first internal electrode containing an electrode active material is provided on the first main surface of the solid electrolyte layer, A solid-state battery characterized by comprising a second internal electrode provided on the second main surface of the solid electrolyte layer and containing an electrode active material.

2. The all-solid-state battery according to claim 1, characterized in that, in the above composition formula, "x" is 0.7 or less.

3. The all-solid-state battery according to claim 1 or 2, characterized in that, in the above composition formula, "y" is 0.3 or less.

4. The compositional formula is Li １＋ｘ＋２ｙ＋ａ A ｙ M′ ｘ M″ ２－ｘ－ｙ P ３ O １２＋ｃ represented by, wherein "A" contains either Mg or Ba, "M′" contains Al, "M″" contains Ge, and a NASICON-type crystal structure satisfying 0.1 ≦ a ≦ 0.3, 0.3 ≦ x ≦ 0.8, and 0.02 ≦ y ≦ 0.

4. A green sheet containing a powder of an oxide-based solid electrolyte, a paste coating for a first electrode layer formed on the first main surface of the green sheet and containing an electrode active material, and a paste coating for a second electrode layer formed on the second main surface of the green sheet and containing an electrode active material. A step of preparing a laminate having the above components is carried out. A method for manufacturing an all-solid-state battery, characterized by comprising the step of firing the laminate.

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